1. Field of the Invention
This invention relates generally to the field of semiconductor device manufacturing and, more particularly, to a method and apparatus for monitoring material removal tool performance using endpoint time removal rate determination.
2. Description of the Related art
There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably. These demands have resulted in a continual improvement in the manufacture of semiconductor devices, e.g., transistors, as well as in the manufacture of integrated circuit devices incorporating such transistors. Additionally, reducing the defects in the manufacture of the components of a typical transistor also lowers the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
The technologies underlying semiconductor processing tools have attracted increased attention over the last several years, resulting in substantial refinements. However, despite the advances made in this area, many of the processing tools that are currently commercially available suffer certain deficiencies. In particular, such tools often lack advanced process data monitoring capabilities, such as the ability to provide historical parametric data in a user-friendly format, as well as event logging, real-time graphical display of both current processing parameters and the processing parameters of the entire run, and remote, i.e., local site and worldwide, monitoring. These deficiencies can engender nonoptimal control of critical processing parameters, such as throughput, accuracy, stability and repeatability, processing temperatures, mechanical tool parameters, and the like. This variability manifests itself as within-run disparities, run-to-run disparities and tool-to-tool disparities that can propagate into deviations in product quality and performance, whereas an ideal monitoring and diagnostics system for such tools would provide a means of monitoring this variability, as well as providing means for optimizing control of critical parameters.
One important aspect in semiconductor device manufacturing is the control of material removal processes, such as etching and polishing. Generally, most features on a semiconductor device are formed by depositing layers of material (e.g., conductive or insulative) and patterning the layers using photolithography and etch processes. Polishing processes are employed to planarize surfaces between various material depositing, steps. There are many variables that affect the accuracy and repeatability of the material removal processes used to form the features. One particular type of material removal tool uses a plasma etch process to perform a primarily anisotropic etch to form features on a semiconductor wafer. Certain etch recipes involve controlling the duration of the etch using a predetermined time. For such a timed etch to be robust, the etch rate of the tool must be predictable and repeatable. Other etch recipes proceed with the etch until an endpoint determination is made. Various techniques are available for detecting etch endpoints. For example, during a plasma etch process the plasma chemistry noticeably changes when a top layer is etched through and the tool begins to etch the underlying layer. The chemistry of the etch chamber is monitored, using for instance an optical emission spectrometer, and the etch is terminated when the change in chemistry is detected. Some etching processes involve the use of both a times etch process to remove the bulk of the material and an endpoint determination process to determine when processing is complete.
It is also common to determine endpoint times for polishing operations. Commonly used endpoint time detection techniques include monitoring motor parameters on the polishing tool, vibration, and characteristics of the wafers being polished. For example, the torque on the polishing motor may increase or decrease when an underlying layer is reached.
As technology improvements facilitate smaller critical dimensions for semiconductor devices, the need for reduction of errors increases dramatically. Proper formation of subsections within a semiconductor device is an important factor in ensuring proper performance of the manufactured semiconductor device. Critical dimensions of the sub-sections generally have to be within a predetermined acceptable margin of error for semiconductor devices to be within acceptable manufacturing quality.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
One aspect of the present invention is seen in a method for monitoring the performance of a material removal tool. The method includes providing a wafer having at least one process layer formed thereon; measuring the thickness of the process layer; removing at least a portion of the process layer in the material removal tool until an endpoint of the removal process is reached; determining a removal rate based on the measured thickness of the process layer and a duration of the removal process until the endpoint is reached; and comparing the determined removal rate to an expected removal rate to monitor the performance of the material removal tool.
Another aspect of the present invention is seen in a processing line including a metrology tool, a material removal tool, and a process controller. The metrology tool is adapted to measure a thickness of a process layer formed on a wafer. The material removal tool is adapted to remove at least a portion of the process layer until an endpoint time is reached. The process controller is adapted to determine a removal rate based on the measured thickness of the process layer and a duration of the removal process until the endpoint is reached and compare the determined removal rate to an expected removal rate to monitor the performance of the material removal tool.